The present invention relates generally to imaging systems and more particularly to a method to improve the display of temporal changes, imaging devices, such as x-ray machines, are widely used in both medical and industrial applications. Imaging devices often use temporal processing to track change in an object over time.
Temporal processing systems typically include the following general modules: acquisition storage module, segmentation module, registration module, comparison module, and reporting module. The input images are 1-D, 2-D, 3-D, derived, synthesized, or montaged, where multiple separate images from a single time point are combined to provide a larger composite, seamless image. Additionally, 1-D images can be montaged to produce 2-D and 3-D images, for example a CT scout-view.
The detection of change in medical images of a patient acquired at two different instances in time has great potential for improving diagnosis. The advent of digital imaging allows computer-assisted detection and identification of these changes and the creation of a xe2x80x9cdissimilarity imagexe2x80x9d containing the change information. This dissimilarity image can be read by a human reader or can become the input to an automated analysis device such as a CAD (computer assisted diagnosis) algorithm.
Currently, as part of Mitsubishi Space Software""s xe2x80x9ctemporal subtractionxe2x80x9d application, dissimilarity images are calculated using a simple pixel-by-pixel subtraction of registered images. Simple subtraction, however, results in images with poor contrast, and is not substantially robust when the two initial images are acquired using different techniques. Simple subtraction also does not incorporate an indication of the confidence in the magnitude of the dissimilarity measurement.
For a temporal subtraction image, the resulting pixel values (and hence the displayed gray-levels) are proportional to the difference or dissimilarity in pixel value between two input images acquired with temporal separation.
Input images are often registered and processed to compensate for several factors such as: the difference in positioning of the subject during the two image the difference in acquisition parameters, the difference in the bit resolution of the images, and the differences in any pre or post processing that may have been applied to the images.
Any errors in registration of the two images may result in significantly large values in the dissimilarity image. For example, if the resulting registration is not perfect, the temporal analysis image of a subject that is identical at both imaging times, is not uniform whereas the desired result is an image with no contrast. Non-zero elements appear at the positions where the registration was not exact. These non-zero elements represent artifacts that could be mistaken for a temporal change in the subject.
Even an ideal registration algorithm produces artifacts, if for no other reason than noise in the image acquisition process. With a poorly chosen display mapping, differences in the noise texture between the two temporally separated images are visible and potentially distracting to the observer. In the case of imperfect registration, it is possible that errors in registration will be displayed with higher contrast than physical changes in the patient.
The disadvantages associated with current, imaging systems have made it apparent that a new technique for temporal processing and display is needed. The new technique should substantially increase accuracy of information acquired obtained from temporal processing. The present invention is directed to this end.
In accordance with one aspect of the present invention, a temporal image processing system includes a temporal processing controller adapted to receive a first image signal and a second image signal from an image controller. The temporal processing controller includes a registration module adapted to register a region of interest of the first image signal and the second image signal and generate therefrom a registration signal. The temporal processing controller further includes a confidence module adapted to receive the registration signal and further adapted to determine a confidence map therefrom. The confidence map is adapted to enhance a contrast of a temporal change in the object relative to a contrast due to at least one misregistration.
In accordance with another aspect of the present invention, a temporal image processing method includes scanning an object and generating a first image signal and a second image signal therefrom. The method further includes receiving the first image signal and the second image signal in a registration module and registering at least one region of interest of the first image signal and the second image signal such that at least one cost signal is generated. A confidence map is generated from the cost signal thereby enhancing a temporal change contrast between the first image signal and the second image signal. At least one distinction is generated between a contrast of temporal changes between the first image signal and the second image signal and a contrast resultant from at least one misregistration.
Additional advantages and features of the present invention will become apparent from the description that follows and may be realized by the instrumentalities and combinations particularly pointed out in the appended claims, taken in conjunction with the accompanying drawings.